Audiolabyrinth,
If you want a processor that sounds great with stereo music and with 5.1 or 7.1 master audio BluRay discs, buy an Evo 707. If you plan to use the unit for stereo music only, you don't need the Evo 707. If that is the case, you might want to try to find a Krell Evo 2. But, either unit would match up perfectly with your amp. I think you would be happy with either choice.
Are you looking for a 2 channel music only pre-amp or a music and home theater processor?
Yes, I do think the Krell Evo 707 will compete very well with the best pre-amps available today.
If you are not using Cast, make sure you are using a high end balanced connection for your audio. I felt Cast MMF made a subtle but perceptible improvement in sound, (faster, more immediate, more vibrant). My 707 is connected to all of my amps with Cast MMF cable. Some people have reported that they like balanced connections better than Cast. I prefer Cast. It's a matter of taste, I guess.
For digital I use an Esoteric K01 SACD/CD player. The K01 is my second most all time favorite piece of equipment. It is far superior to any other SACD/CD player I have ever owned or listened to. I use analog out and connect to the 707 with a Kimber Kable KS1136 (balanced). For BluRay player I have a Dennon 3800 connected with HDMI. An update on the Dennon is way over-due, but I will probably wait for the high end 4K units to hit the market before buying a new movie/disc player.
I would never say the Evo 707 is the last processor I would ever purchase. At this time, I am completely satisfied with the 707, but who knows what the future holds. Something is bound to show up some day that will compel me to update. Unfortunately, Krell has no current plan to out-do the audio section of the Evo 707. I doubt they ever will, unless they feel there is a market that justifies the development and production cost.
I Update components of my audio/home theater system when I find a compelling product and the mood strikes.
When building a great sounding music/home theater system everything is important (front end, cables, pre-amps, amps, speakers, subs., speaker placement, seating placement, set-up, shelving, room acoustics, dedicated lines, eliminating hum, 'dirty lines', RFI). But, I have found that pre-amps have a greater impact on sound quality than amps and cables. A great pre-amp can contribute to a huge improvement in sound.
By the way, your amp should be using dedicated lines (Krell recommends dedicated lines for the 700cx).
Here is another simple, inexpensive tip: Switching from Comcast cable to Verizon FIOS dramatically improved my entire system (music, movies, TV). It eliminated a very soft, barely perceptible but constant hum (mild RFI from the cable lines). I had to put my ear next to the speaker to hear it, but it was always present. Because the FIOS signal is light until it reaches my house, it does not carry RFI (or at least it is less susceptible to RFI). When I switched to FIOS my entire system become incredibly silent with respect to back ground hum or hiss. It improved sound staging, instrument separation and became more 3 dimensional. Any back ground noise will reduce the performance of a high end music system.